The present invention relates to a technique that provides a frequency converter to supply electric power to, for example, a motor, etc.
In a frequency converter, a power element semiconductor device comprising IGBT, diode, etc. to perform frequency conversion ordinarily generates a large quantity of heat, and thus performs forced cooling making use of suction and exhaust with a fan to radiate heat from a radiating section.
In some cases, however, heat cannot be adequately radiated from the radiating section by means of the fan, so that temperature inside a housing rises to cause temperature rise in other elements than the power element semiconductor device.
In particular, since a semiconductor device, such as CPU, etc., for control has a low temperature for guarantee of normal performance (the temperature is referred below to as performance guaranteed temperature) as compared with a power element semiconductor, etc., it is shortened in service life when reaching a high temperature and it cannot in some cases perform control normally due to thermal runaway that accompanies temperature rise, or the like.
It is generally said that semiconductor devices are broken when temperature exceeds about 150° C., and a contrivance for efficient radiation of heat is effected on semiconductor devices such as CPU, etc., which is disclosed in, for example, JP-A-7-95771.
JP-A-7-95771 discloses techniques, in which other products used at low temperatures, than semiconductor devices for electric power are taken the heat from by a cooling action of a cooling fan for cooling of semiconductor devices for electric power.